Anthropometry:
This is a science that studies the dimensions of all our body parts so that products, furniture, and workstations can be designed to fit different sizes of people. It measures all our dimensions and makes recommendations about how to best apply that information.

For example, it would be used to determine the best height for a child's backpack so it can fit the child's back length.

check this out: Fundamental Anthropometric Data  by  http://home.earthlink.net/~stevejg/GSWE.html

Backpackers